1. Field of the Invention
The present invention relates to light-weight tubeless pneumatic tires having excellent anti-airleak properties.
2. Description of Related Art
A typical structure of a tubeless pneumatic tire is shown in FIG. 10.
The tubeless tire includes a carcass ply 1 defining the carcass of the tire and comprising a carcass cord web made of organic fiber such as of nylon, steel wire or the like and a topping rubber covering the opposite surfaces of the carcass cord web. The carcass ply 1 extends from a tread portion through a shoulder portion and sidewall portion to a bead portion, and is turned up around a bead core 2 outwardly from the inside of the tire in the axial direction. The entire interior surface of the carcass ply 1 is lined with an inner liner 3 mainly made of butyl rubber which is excellent in air impermeability for the prevention of air charged in the tired from leaking there from, whereby the tubeless tire maintains a predetermined air pressure therein. As shown in FIG. 10, the tire further includes a tread reinforcing belt 4 such as a breaker or belt layer disposed on the outer surface of the carcass ply 1, and a rim 5.
Such a tubeless tire is light in weight because it has no tube, and in recent years, a further weight reduction of tires has been desired for achieving an energy-saving when the vehicle is operated.
Japanese Unexamined Patent Publication No. 4-90902 (1992) discloses a tubeless pneumatic tire which is made light by separately disposing there in inner liners in regions of the right and left sidewall portions thereof, i.e., by providing no inner liner in a region of the tread portion thereof. However, the major part of the interior surface of the tire is still lined with the inner liner and, therefore, the weight reduction of the tire is not significant.
On the other hand, Japanese Unexamined Patent Publication No. 6-156007 (1994) discloses a tubeless pneumatic tire comprising a carcass 9 consisting of a carcass cord web 7 and a topping rubber 8 of a butyl-based rubber covering the opposite surfaces of the carcass cord web 7, as shown in FIG. 11 (enlarged view of a bead portion) and FIG. 12 (sectional view of the carcass). In FIG. 11, reference numeral 10 denotes the bead core. Since the topping rubber 8 is formed of a butyl-based rubber which is excellent in air impermeability, and hence the carcass 9 per se exhibits the function of an inner liner, the inner liner can be entirely dispensed with. Thus, a satisfactory weight reduction can be achieved.
However, butyl-based rubbers have poor vulcanizability and adhesiveness in comparison with diene-based rubbers. If a tire has a topping rubber 8 entirely formed of a butyl-based rubber, the butyl-based rubber comes into contact with a ply layer (e.g., breaker ply, sidewall rubber or the like) disposed outside the carcass. This may cause the ply layer to be readily separated from the carcass, thereby causing a deterioration the durability of the tire.
It is an object of the present invention to provide a tubeless pneumatic tire that is made lighter by eliminating an inner liner without causing deterioration in the durability thereof.
In accordance with the present invention, there is provided a tubeless pneumatic tire comprising a carcass having a carcass cord web and topping rubber layers covering the opposite sides of the carcass cord web, the carcass extending from a tread portion through a sidewall portion to a bead portion and turned up around a bead core outwardly from inside of the tire in the axial direction of the tire, wherein only the inner one of the topping rubber layers is formed of a butyl-based rubber.
The carcass may include a single carcass ply or, alternatively, a plurality of carcass plies.
Where the carcass includes a plurality of carcass plies stacked one on another, only the inner one of the topping rubber layers of the innermost carcass ply is formed of the butyl-based rubber.
A tubeless tire having the carcass composed of a plurality of carcass plies stacked one on the other may include an innermost carcass ply extending from the tread portion through the sidewall portion to the bead portion and turned up around the bead core outwardly from inside of the tire in the axial direction of the tire, and an outer carcass ply extending from the tread portion through the sidewall portion to the bead portion and turned up around the bead core inwardly from outside of the tire in the axial direction so as to cover the turned-up portion of the innermost carcass ply, wherein only the inner one of the topping rubber layers of the innermost carcass ply is formed with a butyl-based rubber.
A tubeless tire having a carcass composed of a plurality of carcass plies stacked one on the other may include an outer carcass ply extending from the tread portion through the sidewall portion to the bead portion and turned up around the bead core outwardly from inside of the tire, an innermost carcass ply extending from the tread portion through the sidewall portion to the bead portion and terminating at the bead portion without being turned up around the bead core, and a bead apex rubber provided in that portion surrounded by the turned-up portion of the carcass and the bead core, wherein the difference Hc between radial distance Hb from the terminating end of the innermost carcass ply to a radially inside edge of the bead core and radial distance Ha from a radially outside edge of the bead apex rubber to the radially inside edge of the bead core is not less than 5 mm, and wherein only the inner one of the topping rubber layers of the innermost carcass ply is formed of the butyl-based rubber. The radial distance Hb from the terminating end of the innermost carcass ply to the radially inside edge of the bead core is preferably not greater than 20 mm.
In a tubeless tire having a carcass composed of a plurality of carcass plies stacked one on the other, the innermost carcass ply may be divided into two separate carcass ply portions, which are respectively disposed in regions corresponding to the opposite sidewall portions. The two carcass ply portions of the innermost carcass ply are preferably arranged so as to satisfy the following relation:
0.2Wbxe2x89xa6Wnxe2x89xa60.95Wb
where Wb is a tread width and Wn is a spacing between the two carcass ply portions of the innermost carcass ply.
In the tubeless pneumatic tire of the present invention, the aforesaid butyl-based rubber may include a butyl rubber or a derivative thereof as a main ingredient in an amount of not less than 60% by weight. The rubber gage Y between the carcass cord web and the interior surface of the tire may be about 0.8 mm to about 2.5 mm. The tubeless tire preferably includes a reinforcing rubber layer provided outside the turned-up portion of the carcass.
Further, the tubeless pneumatic tire of the present invention may include an inner liner covering the inner surface of the carcass. Alternatively, the topping rubber layer formed of the butyl-based rubber may define the interior surface of the tire without the inner liner being provided on the inner surface of the carcass.
Since the inner topping rubber layer of the carcass is formed of the butyl-based rubber which is excellent in air impermeability in accordance with the present invention, the tubeless pneumatic tire has an anti-airleak property comparable or superior to the conventional tubeless pneumatic tires and offers a lighter weight when it is not lined with an inner liner.
The tubeless pneumatic tire having the carcass composed of the plurality of carcass plies has an excellent anti-airleak property and a light weight while ensuring stable steering performance. In particular, the provision of the innermost carcass ply of the separation type realizes a further weight reduction of the tubeless pneumatic tire.
The lining of the inner topping rubber layer of the carcass with an inner liner further improves the anti-airleak property of the tubeless tire of the present invention.
Further, the provision of the reinforcing rubber layer improves the durability of the tubeless tire without increasing the weight of the tire very much.
These and other objects, and advantages of the present invention will become apparent from the following detailed description.